Tissue samples of whole body white sucker (Catostomus commersoni) were collected at 15 sites and smallmouth bass (Micropterus dolomieu) were collected at 5 sites during 1992 in the Lower Susquehanna River Basin to determine the occurrence and distribution of 28 selected organochlorine compounds as part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program. Only 12 of the 28 compounds occurred at concentrations greater than the 5 µg/kg reporting limit (total PCB’s reporting limit is ‹50 µg/kg and toxaphene is ‹200 µg/kg). The most frequently reported compounds were p,p’-DDE (reported in all tissue samples), total polychlorinated biphenyls (PCB’s), and trans-nonachlor.

High concentrations of p,p’-DDE and low concentrations of the other DDT metabolites for the Lower Susquehanna River sites indicate no recent influx of DDT. Comparison with historical data from the Lower Susquehanna River Basin shows a decline of organochlorine concentrations within the basin. In 1987, Quittapahilla Creek had the highest concentrations of p,p’-DDE in a national survey of contaminant occurrence in fish tissue conducted by the U.S. Environmental Protection Agency. This stream ranked the highest for total DDT of the 20 NAWQA studies started nationally in 1991. Total DDT concentrations were higher in agriculture-dominated (>50 percent) sites than in forest-dominated (>50 percent) sites with the exception of Deer Creek and Big Beaver Creek. These two sites are located more in grazing areas that lack a substantial crop-land use. Concentrations of total PCB’s were highest in basins with greater than 10 percent urban land use excluding the larger river sites. Concentrations of total chlordane were highest at sites with greater than 70 percent agricultural and 10 percent urban land use.

Regional comparisons of total DDT, total PCB’s, and total chlordane in white sucker tissue from the Lower Susquehanna, Hudson (in New York), and Connecticut River Basins showed that median concentrations of total DDT were different (p=0.05), with the Lower Susquehanna Basin being the lowest. Total PCB’s and total chlordane medians were similar. Comparison of the data from national and regional studies with data from this local study showed concentrations of p,p’-DDE in the Lower Susquehanna River Basin are similar to those nationwide and lower than the concentrations measured in the Northeast. PCB concentrations in the Lower Susquehanna River Basin and the Northeast were higher than those nationwide.